This invention is concerned with a closure assembly for a container, particularly a plastic container and a method for forming said closure.
In the past aerosol containers have been fabricated from metals. However, such metal containers suffer from certain disadvantages. They are subject to rusting and denting and are relatively heavy. If bursting or exploding of the container occurs due to excessive pressures there is the danger of injury.
More recently the aerosol industry has moved towards the use of plastic aerosol containers made from materials such as polyethylene terephthalate which offers the advantages of freedom from rusting and denting, light weight, amenability to graphics for purposes of trade dress and good tactile properties, among others. However, one of the problems associated with the commercial production of these aerosol containers is the provision of an effective closure. Metal mounting cups have been used which fit onto the container opening. In one method of closure the cup is clinched externally around the neck of the container by segmented metal jaws such as those used to seal glass bottles. In another method, the skirt of the metal cup is tucked under a bead on the container neck by rotating the container or the tool used to form the seal. The cups employed in the clinched jaw method are subject to leakage between the clinched portions and in the case of both the clinched jaw and roating methods the cup cannot easily be removed if, for example, the plastic container is required to be recycled separately from the cup.
Another type of closure used on metal cans and containers is the so-called double seam closure. In this type of closure the top of the container body terminates in a flange which fits within a curl or tuck on the peripheral edge of the mounting cup. In forming the double seam the flange is interfolded with the curl in a rotating method involving the tool or the container as discussed above to hermetically seal and close the container as the double seam is formed. In addition a small amount of sealing compound is positioned along the interior wall of the curl to provide a hermetic seal in forming the double seam. Such double seam closures are not effective on plastic containers because the plastic cannot be readily interfolded with the curl of the metal mounting cup and deformation of the container top occurs. Further, neither the segmented jaw method nor the rotating method allow charging of the container under the mounting cup. Such charging can only be accomplished through the aerosol container valve.
The present invention, on the other hand, provides an effective closure for a plastic container which employs a metal mounting cup to seal the container but is not sealed with segmented jaws or by the rotation method. The cup can more easily be removed without damage to the container for recycling purposes than in the case of clinched closures or double seam closures. In addition the invention permits charging of the aerosol container under the cup and therefore lends itself to a retrofit of existing under the cup charging equipment used to charge metal containers.